Portable X-ray spectrometer

ABSTRACT

A portable X-ray spectrometer consisting of a case with a partial vacuum of 10 1 to 10 3 Torrs inside it, and containing a sample holder, glow-tube with low-temperature cathode, dispersion crystal, goniometric device and detector, an internal-combustion engine, a partial vacuum pump driven by this engine, and a lowpowered source of electricity.

United States Patent Sahores et al.

PORTABLE X-RAY SPECTROMETER inventors: Jean Sahores; Etienne Larribau, both of Pau, France Assignee: Societe Nationale des Petroles dAquitaine, Courbevoie, France Filed: Mar. 16, 1973 Appl. No.: 342,279

Foreign Application Priority Data Mar. 17, 1972 France 7209419 US. Cl. 250/310; 250/306 Int. Cl. HOlj 37/26 Field of Search 250/272, 273, 306, 307,

References Cited UNITED STATES PATENTS 9/1948 Friedman 250/272 Nov. 11, 1975 2.837.656 6/1958 Hcndce Ct 211 250/272 3.435.211 3/1969 Softky 250/272 1471.694 10/1969 Poen 250/310 Primary E.\'aminer lames W. Lawrence Assistant E.\'aminerB. C. Anderson Attorney, Agent, or Firm-Brisebois & Kruger [57] ABSTRACT A portable X-ray spectrometer consisting of a case with a partial vacuum of 10 to 10 Torrs inside it, and containing a sample holder, glow-tube with lowtemperature cathode, dispersion crystal, goniometric device and detector, an internal-combustion engine, a partial vacuum pump driven by this engine, and a lowpowered source of electricity.

7 Claims, 6 Drawing Figures US. Patent N0v.11,1975 SheetlofZ 3,919,549

I ///////l V/// US. Patent- N0v.11,1975 Sheet2of2 3,919,549

PRIOR HRT l d I ELECTRON/C $17.4. l0 ourpur UNIT cou 1N6- \SPECTROMETEE PUMP 7W0 CYCLE PORTABLE X-RAY SPECTROMETER This invention concerns a compact, lightweight portable X-ray spectrometer. Such spectrometers can be used in the field, and offer the advantage of not requiring bulky, awkward sources of power such as liquefied gas or high-voltage electric current.

Conventional appliances, with a tube excited by fluorescence and a dispersion crystal, are not sensitive enough unless powered by high-voltage, high-amperage current. Appliances using radio-active sources, the small capacity of which excludes dispersion by crystal and requires analysis by energy discrimination, have poor separating power.

The X-ray spectrometer described in this invention overcomes these drawbacks by using glow-tubes with a high energy efficiency that do not require any high voltage power supply, tube-cooling system, or highcapacity vacuum pump.

The invention is illustrated in the accompanying drawings, in which:

FIG. 1 is an overall view of the case with instruments it contains,

FIG. la shows in detail how the main casing is attached to the base;

FIG. lb shows in detail the assembly of the sampleholder disc and its removable casing; I

FIG. 2 is a schematic perspective view illustrating one type of cold cathode gas suitable for use in carrying out the invention;

FIG. 3 is an axial sectional view illustrating another type of cold cathodezgas tube suitable for use in carrying out the invention; and

FIG. 4 is a schematic assembly view showing a spectrometer according to the invention connected to its electrical supply and vacuum pump. 1

Such cold cathode gas tubes include one described in greater detail in my copending application Ser. No. 318,198 and illustrated in FIG. 2 emitting both electrons and X-rays, and operating in a partial vacuum of 10 to form 1 Torrs, consisting of a sleeve 4 containing a low-temperature cathode b, an anode c and a target d. An opening in the cover, near the targ et, allows secondary electrons and X-rays to pass, without any intervening window, into the sample chamber, which is under the samepartial vacuum as the inside of the tube. The flux is stabilized by a flow of gas, the rate of which depends on the flux emitted, without any need for regulating grids, which require higher-voltage current. Another tube described in greater detail in my copending application Ser. No. 318,199 and illustrated in FIG. 3 that can be used in this portable spectrometer is a glow-tube emitting electrons directly. It also operates in a partial vacuum, and stabilization is obtained by controlling the flow of gas. The low-temperature cathode b consists of a metal disc or ring, fed with a fairly low voltage, of about kV, while the grid-shaped anode c ensures a rectilinear trajectory for the electron flux striking the sample d directly.

This portable X-ray spectrometer (illustrated in FIG. 4) comprises a compact case e containing a sample holder, glow-tube with low-temperature cathode emitting electrons or both electrons and X-rays, dispersion crystal, goniometric device, and detector, an internal combustion engine g, a partial-vacuum pump fdriven by this engine, and a low-powered source of electricity h.

2 The case is compact and light enough to be used in the field: the tube weighs onlya fraction of the weight of conventional tubes, and the absence ofa cooling circuit means a saving of approximately 50 kg.

The partial vacuum, of approximately 10 to 10 Torrs, ismaintaincd by a pump, such as a blade pump with an output of several cubic m/hr. This pump is only cause of the absence of ignition circuit. This makes it particularly suitable for use in the spectrometer, because in analysing traces the quality of the background noise of the electronic countingdevice is seriously affected by such interference. I

The power source and the system supplying current to the tube electrodes can be considerably reduced in scale, because of the low consumption of the glowtube. The stabilization system comprises a transformer and high-voltage regulator to keep it stable, regardless of the charge between anode, and cathode. Electricity can be supplied by a 200 watt generator, driven by the vacuum-pump engine, notably when it has to feed a buffer battery and power the electronic spectrometer output unit; in other cases, lower-powered sources, of to watts for example, are sufficient, and can consist of batteries. I

The cold cathode gas-tube: with high radiation yield allows a dispersion crystal to be used. Any dispersion system requiresahigh radiation intensity, because of the considerable loss of radiation when selected by diffraction. Existing portable spectrometers, using lowyield radiation sources, are not suitable for use with a dispersion system, which has a low reflecting capacity, in other words information output, so that their resolving poweris confined to that of their detector (approximately 300 to 400 eV). In practice, there are many cases in which this is inadequate, so that there is bound to be confusion of the analytic lines, such as Ca and K, or Ni and Co. Spectrometers using conventional tubes which have a low radiation yield and satisfactory resolving capacity, because of their crystal dispersive system, have to be provided with high sources of energy, too heavy and cumbersome to be suitable for carrying.

Because of the reduction in the energy of the X-rays, from 60 KeV for a conventional tube to 5 KeV for coldcathode gas-tubes, anti-radiation protection of the spectrometer itself can more or less be dropped. The strength of a case of this kind, which is subject only to partial vacuum, does not require any special precautions as regards the material used, and laminated glass fibre is recommended. This ensures perfect mechanical properties, and a considerable reduction in weight.

It will be easier to understand the invention from the following description, illustrated by the accompanying figures.

The case containing the instruments and forming a hermetic enclosure consists of three parts a rigid lightalloy base 1, a parallelepiped-shaped main cover 2, and a semi-cylindrical cover 3, both made from laminated glass fibre.

The base 1 is fitted with a stand 4, handle 5, and a continuous groove 6 runs round the opposite side of the base from the stand and handle attachments. The base also has two apertures 7 and 8 fitted with seals and situated on its longitudinal axis, two holes 9 and 10 with electrical insulation, another aperture 11, and a rectangular opening 12, situated below the lower aperture, 8 with a groove 13 running round it on the same side of the base as the stand and handle attachments. The edge of the main cover 2 fits into the groove 6 on the base, with a seal between them, and the edge of the semicylindrical cover 3 fits into the other groove 13, with a seal between them 15. The two covers are held in position by attachments not shown here. The base 1 carries a cold-cathode glow-tube and coaxial collimators 16, on an axis parallel to the longitudinal axis of the base, an analyser crystal 17, which can be adjusted by a shaft 18 passing through the upper aperture 7, a goniometric device 19 the shaft 20 of which is concentric with the shaft 18 for the crystal, and which also passes through the aperture 7, a detector 21 connected to the goniometric device, and a sample-holder disc 22, which passes through the rectangular opening 12, and comprises a control system with a bevel gear 23. The vertical axis 24 of this disc passes through a plate 25 on the base 1, with a circular opening 12, positioned on the axis of the glow-tube and corresponding to the position in which a sample 27 beneath it can be observed.

The cold cathode gas-tube 16 is connected through the hole 9 to a high-voltage source of electricity (not shown here). The receiver 20 is connected to an electronic output unit i illustrated in FIG. 4, through the hole 10. The space between the base 1 and the two covers 2 and 3 is connected through the other aperture 11 to a vacuum pump, driven by a two-stroke or self-ignition internal combustion engine (not shown here).

To use the apparatus, the various instruments are checked, the cover 2 is placed in the groove 6 and locked in position, the sample-holder disc is loaded, the other cover 3 is placed in its groove 13 and locked,and a partial vacuum is set up in the enclosure thus formed.

When measurements have been carried out on one series of samples, the pressure in the enclosure is brought up to atmospheric pressure, and the semicylindrical casing is removed, so that the samples can be replaced for a new series of measurements.

What is claimed is:

l. A portable X-ray spectrometer comprising:

4 a casing capable of supporting a partial vacuum of IO to 10" torrs .in a chamber defined therewithin, a sample holder within said casing for supporting samples to be analyzed, 3

a cold cathode gas tube having a grid shaped anode and a low temperature cathode adapted to operate on a supply voltage as low as about SkV, both spaced from said sample holder and positioned to project an electron beam against a sample supported by said sample holder in alignment with said cathode and anode,

an analyzing crystal positioned to receive X-ray radiation from said sample, 7 goniometric means positioned to receive X-ray radiation reflected from said crystal,

said goniometric means, analyzing crystal, sample holder and gas tube all lying in a unitary common atmosphere defined within said casing.

2. A portable X-ray spectrometer as claimed in claim 1 in which said sample holder and analyzing crystal lie at opposite ends of said tube, which is provided with a central passage through which radiation from a sample on said sample holder is reflected to said crystal.

3. A portable X-ray spectrometer as claimed in claim 1 in which said casing comprises a detachable part and said sample holder extends into said detachable part so that removal of said detachable part affords access to said casing.

4. Spectrometer as claimed in claim 1 comprising a low-power generator, connected to supply said tube, a pump connected to maintain a partial. vacuum within said casing, and a non-electrically ignited engine connected to drive said pump.

5. Spectrometer as claimed in claim 4 in which said engine is also connected to drive said generating system.

6. Spectrometer'as claimed in claim 4 in which said engine is a two-stroke self-igniting motor.

7. Spectrometer as claimed in claim 1 in which said casing comprises a rigid lightweight alloy base carrying said measuring means, analyzing crystal, sample holder and tube, said base being provided with sealed openings admitting wires supplying the tube and measuring means, and admitting a pipe for evacuation of said chamber, together with a cover which fits and is sealed into a groove running around the periphery of the base. 

1. A portable X-ray spectrometer comprising: a casing capable of supporting a partial vacuum of 10 1 to 10 3 torrs in a chamber defined therewithin, a sample holder within said casing for supporting samples to be analyzed, a cold cathode gas tube having a grid shaped anode and a low temperature cathode adapted to operate on a supply voltage as low as about 5kV, both spaced from said sample holder and positioned to project an electron beam against a sample supported by said sample holder in alignment with said cathode and anode, an analyzing crystal positioned to receive X-ray radiation from said sample, goniometric means positioned to receive X-ray radiation reflected from said crystal, said goniometric means, analyzing crystal, sample holder and gas tube all lying in a unitary common atmosphere defined within said casing.
 2. A portable X-ray spectrometer as claimed in claim 1 in which said sample holder and analyzing crystal lie at opposite ends of said tube, which is provided with a central passage through which radiation from a sample on said sample holder is reflected to said crystal.
 3. A portable X-ray spectrometer as claimed in claim 1 in which said casing comprises a detachable part and said sample holder extends into said detachable part so that removal of said detachable part affords access to said casing.
 4. Spectrometer as claimed in claim 1 comprising a low-power generator, connected to supply said tube, a pump connected to maintain a partial vacuum within said casing, and a non-eleCtrically ignited engine connected to drive said pump.
 5. Spectrometer as claimed in claim 4 in which said engine is also connected to drive said generating system.
 6. Spectrometer as claimed in claim 4 in which said engine is a two-stroke self-igniting motor.
 7. Spectrometer as claimed in claim 1 in which said casing comprises a rigid lightweight alloy base carrying said measuring means, analyzing crystal, sample holder and tube, said base being provided with sealed openings admitting wires supplying the tube and measuring means, and admitting a pipe for evacuation of said chamber, together with a cover which fits and is sealed into a groove running around the periphery of the base. 